1. Field of the Invention
The invention relates generally to crop harvesting headers and more particularly to an improved system for mounting and counterbalancing a floating cutterbar on a header.
2. Prior Art
Resilient suspension of floating-type cutterbars is well known as evidenced by several U.S. patents: U.S. Pat. Nos. 1,996,294; 2,472,762; 2,795,922; 2,915,870; and 3,982, 383.
While showing a variety of spring arrangements the patents display a common feature. That is, the spring force which counterbalances or supports the cutterbar is variable throughout the moving range of the cutterbar. This is so because the force rate of the springs necessarily varies as the springs flex or expand and contract through their range of movement. For example, the output force of a loaded spring varies linearly with expansion of the spring.
The practical effect of the linear spring rate in floating cutterbars is to produce variable ground pressure of the cutterbar. And this variable ground pressure can have an adverse effect on maintaining a desired cutting height along the length of the cutterbar. This remains true even though the system may include means for pre-adjusting or selecting the cutterbar supporting force as in U.S. Pat. Nos. 2,915,870 or 2,472,762. The problem may thus be summarized in that prior art systems cannot provide a substantially constant ground pressure of a cutterbar with resulting inability to maintain a desired cutting height throughout the range of movement of the cutterbar.